The present invention relates to a generator stator core, more particularly, to a ventilation duct disposed between magnetic laminations of a generator stator core.
The stator core becomes hot during operation of the electric generator and the heat must be removed to keep it from overheating. Cooling the generator stator core is important for reliable generator performance. In the conventional cooling method, the steel core is cooled by a forced-convection flow of air or hydrogen gas via radial space blocks and cooling channels. In general, hot spots usually appear near the tooth tips of the lamination. Conventionally, the gas smoothly flows inside of the cooling channels to remove heat. These space blocks are positioned in such a way to assure tightness of the core during assembly and operation, and not impede or restrict the flow of gas through the stator.
A generator stator core is constructed by stacking layers or xe2x80x9claminationsxe2x80x9d of insulated silicon-iron metal disks together. Inside space blocks or rails are inserted between the layers of the metal disk and these space blocks extend radially from the center of the core. The functions of the inside space blocks are to provide a ventilation passage for a cooling gas and to transfer the load due to axial stacking pressure of the laminators. The space blocks are spaced at regular intervals around the circumference of each metal disk. On a conventional strator lamination 1 of arcuate shape, inside space blocks 2 are typically arranged radially and have a cross-section or profile resembling small I-beams. These I-beam shaped space blocks are spot welded to stator lamination 1 shown in FIGS. 1 and 2. The space blocks are made from one of several materials such as low carbon steel, silicon-manganese bronze, or stainless steel.
Several attempts for enhancing local heat transfer and reducing hot spot temperature in the stator core were made previously. The following patents and applications are hereby incorporated by reference. U.S. Pat. No. 5,869,912 xe2x80x9cDirect-Cooled Dynamoelectric Machine Stator Core with Enhanced Heat Transfer Capabilityxe2x80x9d discloses the use of a turbulator element in ventilation ducts. The spacer blocks have a straight longitudinal profile. Commonly-assigned, co-pending U.S. patent application Ser. No. 09/421,160, filed on Oct. 19, 1999 discloses the use of cylindrical compact posts to maximize the flow area for the cooling gas. U.S. Pat. No. 4,362,960 xe2x80x9cSpacer Assembly for a Stator Venting Duct of an Electric Power Machine,xe2x80x9d discloses slightly curved spacer members having a rectangular profile. While all of these prior art attempts do alleviate the hot spot problems to some extent, the conventional space block shapes and the straight radial configurations do not take maximum advantage of heat transfer principles. Since the search is always on for improved generator performance, there is a particular need to enhance the heat transfer in a generator stator core.
The present invention provides several structural advantages for improving heat transfer along a generator strator core. The various embodiments are based on two fundamental heat transfer principles: imparting turbulence to the cooling flow and increasing surface area. One way that enhanced cooling is achieved is in the arrangement of the space blocks. In general, the space blocks which the prior art arranged in more or less straight lines are configured, in the present invention, in undulating arrangements such as a zigzag or a sinusoidal pattern. These configurations force the cooling gas to change direction as it makes its way through the ventilation pathway. This disturbance in the flow enhances the cooling of the strator core. Another way to enhance cooling is to change the cross-sectional shape of the space blocks to provide more surface area to promote heat transfer. These two main principles are applied in various permutations to optimize the cooling effect of the cooling gas.
More specifically, according to one aspect of the present invention, at least one space block includes a wavy longitudinal profile of a generator stator core. Thus, the cooling gas is influenced to periodically change its direction along the flow path adjacent to the longitudinal profile.
According to another aspect of the present invention, a plurality of vortex generators can be applied in a generator stator core for cooling by punching a plurality of delta-shaped, wedge-shaped, or hemispherical protrusions on laminations. Thus the vortex generator impart turbulence to the cooling flow.
According to another aspect of the present invention, a generator stator core comprises at least one space block including a plurality of thermal fins extending from a side surface of the space block. Thus, the heat transfer surface is increased for the side surface of the space block.
The present invention is advantageous for augmenting the heat transfer for a generator stator core by increasing the cooling capacity at the stator core. Localized hot spots are greatly reduced by the invention. The generator output rating is increased because the stator temperature is controlled at the lower temperature than conventional cooling systems.
These features and advantages of the present invention will be apparent upon consideration of the following detailed description thereof, presented in connection with the following drawings in, which like reference numerals identifying the elements throughout.